The carbon nanotube (hereinafter, referred to as CNT) has a structure in which a graphene sheet is cylindrically wound, and is a material having a one-dimensional structure having a very large aspect ratio (see Nonpatent Document 1). CNT is known to have excellent mechanical strengths, flexibility and further very stable chemical properties. The production methods of CNT reportedly include the arc discharge method, the laser vaporization method and the chemical vapor deposition method (hereinafter, referred to as CVD). Especially, the CVD method is a synthesis method attracting attention as a method suitable for mass synthesis, continuous synthesis and high-purification (refer to R. Saito, and H. Shinohara (coeds.) “Foundation and Application of Carbon Nanotube”, published by Baifukan Co., Ltd.).
Further, a single-walled CNT (hereinafter, referred to as SWNT) is confirmed to exhibit metallic properties and semiconductic properties depending on its winding way and its diameter, and is expected to be applied to electric and electronic devices and the like. The synthesis method of SWNT is predominantly a catalyst CVD method (see, for example, Nonpatent Document 2) to grow nanotubes. The catalyst CVD method involves production using metal nanoparticles as a catalyst. While a gaseous carbon source is supplied, the carbon source is catalytically decomposed at a high temperature to grow nanotubes on the metal nanoparticles. At this time, production is carried out using the nanoparticle catalyst in a state dispersed in a gas phase (hereinafter, referred to as method A). There is also a method in which the nanoparticle catalyst is used in a state loaded on a substrate (hereinafter, referred to as method B). These methods A and B each have advantages and disadvantages.
[About Existing SWNT Production Methods]
FIG. 17 is a diagram showing the outline of the method A (gas phase-dispersed catalyst). Synthesis of SWNT is carried out by simultaneously spraying a catalyst source and a carbon source into an externally heating reactor. Typical synthesis methods classified into the method A include HiPco method (for example, see Nonpatent Document 3) and the like. This method A can effectively utilize the three-dimensional space of the reactor. However, since the catalyst accompanies a reaction gas, the retention time of the catalyst in the reactor is short and the catalyst SWNT, contaminates a reaction product. Further, since the catalyst particles are as small as several nanometers and aggregate rapidly, the space concentration of the catalyst can hardly be raised.
FIG. 18 is a diagram showing the outline of the method B (substrate-loaded catalyst). In the method B, a catalyst is loaded on a substrate; and a carbon source is supplied on the catalyst. Super Growth method (for example, see Nonpatent Document 4) and the like are classified into this method B; and Super Growth method is a typical method B. This method B allows for a high-rate growth. For example, a high-rate growth of 3 mm/10 min is carried out. The catalyst is fixed on the substrate, and contamination of a synthesized SWNT with the catalyst is therefore suppressed. However, since only a planar two-dimensional space of a reactor can be utilized, the space utilization in a reactor is inferior to the method A.
Further, a separation process to separate the synthesized SWNT is required. In the case of mass production of SWNT, repeating use of a substrate with a catalyst attached is indispensable, and this technique has not yet been established. Further, a method is proposed in which Ni is coated on the inner wall of a honeycomb substrate, and carbon nanofibers are grown thereon (Patent Document 1). However, the honeycomb substrate is not for production of carbon nanofibers, but for production of a fixed body in which carbon nanofibers are held densely on the body. The honeycomb substrate itself is mounted on automobiles and the like, and is used as a hydrogen storage body.    Nonpatent Document 1: S. Iijima, Nature 354, 56 (1991)    Nonpatent Document 2: H. Dai, A. G. Rinzler, P. Nikolaev, A. Thess, D. T. Colbert, and R. E. Smalley, Chem. Phys. Lett. 260, 471 (1996)    Nonpatent Document 3: HiPco method: M. J. Bronikowski, P. A. Willis, D. T. Colbert, K. A. Smith, and R. E. Smalley, J. Vac. Sci. Technol. A19, 1800 (2001)    Nonpatent Document 4: K. Hata, D. N. Futaba, K. Mizuno, T. Namai, M. Yumura, and S. Iijima, Science 306, 1362 (2004)    Patent Document 1: Japanese Patent Laid-Open No. 2001-288626